Creates the shared schema module for library evaluation traces
(ADR-022 §4): Zod-validated frontmatter with all 8 filter fields and
enum constraints, plus parseTrace/validateTrace exports and a custom
YAML frontmatter parser for the nested trace format.
Also adds docs/library-decisions/_template.md with all 11 required
headings (8 Filter + 3 Prompt) in machine-checkable ADR-022 order.
Adds zod as a root devDependency so the script is runnable directly
from the workspace root without a package context.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
